In a storage device, such as a magnetic disk device, that has a head for reading and writing data from and into a rotating storage medium, accurate position control of head (hereinafter, position control of head is sometimes simply referred to as “position control”) is necessary to read and write data at a target position.
In the magnetic disk device, head-position control is performed based on position information stored in a servo frame and position-information correction values stored in a post code region. A position-information correction value is a correction value determined based on, for example, the result of Repeatable Run Out (RRO) measurement. In recent years, with the improvement in recording density of the magnetic disk device, a track width tends to be narrower. Therefore, correcting the position of the head with high accuracy based on the position-information correction values has become increasingly important.
However, the position-information correction values stored in the post code region may be destroyed due to some reason. If any position-information correction value is destroyed, the head-position control cannot be appropriately performed, and therefore a serious failure tends to occur, such as side erase.
To prevent the occurrence of a failure due to destruction of a position-information correction value, a technology of providing a parity bit to the position-information correction values has been known. By using this technology, the position-information correction values can be used to perform position control even if any position-information correction value has been destroyed, thereby avoiding the head from being moved to an erroneous position.
However, the conventional technology using the parity bit explained above has a problem of a decrease in accuracy of position control. The reason for this problem is as follows. In the conventional technology using the parity bit explained above, it is possible to prevent the use of the destroyed position-information correction value for position control. However, when a position-information correction value is destroyed, position control is performed based on only the position information.